The exemplary embodiment relates to a method for preparing nanopowders of reactive metals and their hydrides and carbides.
Metal powders which include very small particles have a variety of uses. Currently, materials used for metalizing of energetic formulations are micron-scale aluminum particles. Problems associated with the burn properties of the traditional metal additives in energetic formulations often relate to the burn kinetics/speed being impeded by the metal oxide coating of the particles, which arises naturally from the materials being exposed to air. Passivated nanoscale aluminum-based materials have been explored for use in energetic formulations on an experimental basis.
Another application for metal powders is in the field of energetics where metal powders are pressed into reactive projectiles that will self-ignite on impact with the target, purely from the kinetic energy of the impact. Currently mixtures of aluminum particles and Teflon™ are used for this purpose. The use of hafnium nanoparticles, for example, for underwater energetic applications would be of particular advantage due to the potential of developing high-density materials (Hf has a density of 13.3) that would have great momentum for high-speed underwater penetration. The volumetric combustion energy of Hf is as great as aluminum, and the high density would give a projectile more penetrating power. However, air stable nanoparticles of Hf have proved difficult to produce.
Large-scale production of reactive metal nanoparticles or nanopowders is of interest for applications in powder metallurgy, energetic materials, hydrogen storage materials, tribology, nanocomposites, and ceramics. (Haber, J. A.; Buhro, W. E. J. Am. Chem. Soc. 1998, 120, 10847; Kwon, Y.; Gromov, A. A.; Strokove, J. I. Appl. Surf. Sci. 2007, 253, 5558; Dlott, D. D. Mater. Sci. Tech. 2006, 22, 463; Li, W.; Li, C.; Ma, H.; Chen, J. J. Am. Chem. Soc. 2007, 129, 6710; and Vasquez, Y; Henkes, A. E.; Bauer, J. C.; Schaak, R. E. J. Solid State Chem. 2008, 181, 1509) Rieke originally pioneered alkali metal reduction of various metal salts in solution, but focused on the catalytic activity of various metals in the finely divided state (Furstner, A. Angew. Chem. Int. Ed. Engl. 1993, 32, 164; Rieke, R. D.; Burns, T. P.; Wehmeyer, R. M.; in High Energy Processes in Organometallic Chemistry (Ed.: K. S. Suslick), ACS Symposium Series 1987, 333, 223; Rieke, R. D.; Chao, L. Syn. React. Inorg. Met. Org. Chem. 1974, 4, 101). Disclosed herein is a method suited to bulk production of nanopowders. One popular technique for production of reactive nanopowders is reactive ball-milling. (Barraud, E.; Bégin-Colin, S.; Le Caër, G.; Barres, O., Villeras, F. J. Alloys Compnd. 2008, 456, 224; Yen, B. K. J. Alloys and Compounds 1998, 268, 266).
Vasquez et al. (Vasquez, Y; Henkes, A. E.; Bauer, J. C.; Schaak, R. E. Journal of Solid State Chemistry 2008, 181, 1509-1523) describes the potential of making various metal nanoparticles by low energy solution based methods. Due to air-sensitivity and therefore difficulty in handling, reactive metal nanoparticles (RMNPs) have not been extensively studied, and remain as one of the significant challenges in nanoscience. To date there has only been one reported synthesis of Ti nanoparticles via a solution-phase reduction method. (see Ghosh, D.; Pradhan, S.; Chen, W.; Chen, S., Chemistry of Materials 2008, 20(4), 1248-1250).
Berry has produced Zr nanoparticles by reduction of ZrI4 with LiH with reaction times of weeks followed by annealing up to 600° C. (Berry, A. D.; Stroud, R. M.; Sutto, T. E. Synthesis and characterization of a nanophase zirconium powder. Journal of Materials Chemistry 2003, 13, 2388-2393, hereinafter Berry 2003). The reaction was very slow, however.